Method and device for adapting a threshold value of a detection device

Abstract

A method for adapting a threshold value of a detection device comprising the following steps: Transmission of a signal burst having a predefined pulse-repetition interval, a predefined burst length and a defined signal frequency; receiving and processing of a receive signal, in particular by means of amplification, filtering and demodulation, so as to obtain the envelope; determining a receive-signal magnitude as interference-level sample from the receive signal following a first predefined time duration (Δt 1 ) starting with a signal burst within a predefined second time duration (Δt 2 ), preferably at the end of the pulse repetition interval; and adapting the threshold value of the detection device as a function of the interference level sample. Also provided is a device for adapting a threshold value of a detection device.

1. A method for adapting a threshold value of a detection device, comprising:
 transmitting a signal burst at a predefined pulse-repetition interval, a defined burst length, and a defined signal frequency; 
 receiving and processing a receive signal to obtain an envelope; 
 ascertaining a magnitude of the receive-signal as an interference-level sample from the envelope of the receive signal after a first predefined time duration beginning with the signal burst, and within a predefined second time duration prior to a next signal burst; 
 generating a dynamic threshold value by summing the interference-level sample with a static threshold value having a predefined time characteristic; 
 comparing the envelope of the receive signal to the dynamic threshold value; and 
 generating an output indicating that an object has been detected when the envelope exceeds the dynamic threshold value. 
 
     
     
       2. The method as recited in  claim 1 , wherein:
 the receive signal is amplified, filtered, and demodulated to obtain the envelope. 
 
     
     
       3. The method as recited in  claim 1 , wherein:
 the ascertaining is performed at an end of the pulse-repetition interval. 
 
     
     
       4. The method as recited in  claim 1 , wherein:
 the ascertaining is performed from an envelope of the receive signal by a peak-value rectifier, the peak-value rectifier including a hold-time constant that is greater than the pulse-repetition interval. 
 
     
     
       5. The method as recited in  claim 4 , further comprising:
 configuring the peak-value rectifier so that a load-time constant thereof exceeds the defined burst length, so that a hold-time constant thereof is longer than the pulse-repetition interval, and so that a temporal acquisition duration of the interference-level sample is longer than the load-time constant. 
 
     
     
       6. The method as recited in  claim 1 , wherein a timer stipulates the first predefined time duration at 35 ms to 55 ms, and wherein the timer is triggered at the predefined pulse-repetition interval, at a clock frequency of 15 Hz to 30 Hz. 
     
     
       7. The method as recited in  claim 1 , wherein the static threshold value corresponds to programmed interpolation points within a static characteristics curve. 
     
     
       8. The method as recited in  claim 1 , wherein, for the purpose of an optimal receiver, a signal processing including an I/Q demodulation and a cross-correlation of an I and a Q channels using; an ideal time-shifted and a Doppler-shifted replica of a transmit signal is implemented, and wherein an amount is formed from a sum of squares of the cross-correlation of the I and Q channels, the amount being scaled by an auto-correlation of the replica. 
     
     
       9. The method as recited in  claim 1 , further comprising:
 amplifying the receive signal; 
 filtering the receive signal by a bandpass filter with a mid-frequency on one of a resonant frequency and a transmit frequency of a transducer and with a pass-bandwidth that is proportional to an inverse value of the burst length; 
 demodulating the envelope by a double-way rectifier and a low-pass filter, before the interference-level sample is ascertained therefrom. 
 
     
     
       10. The method as recited in  claim 1 , wherein:
 the ascertaining of the interference-level sample is performed during a time interval in which no reflected measuring signal from a target object occurs. 
 
     
     
       11. The method of  claim 1 ,
 wherein the ascertaining of the interference-level sample is performed only during a time interval in which no reflected measuring signal from a target object occurs. 
 
     
     
       12. A device for adapting a threshold of a detection device, comprising:
 a transmit/receive device for transmitting a transmit burst at a predefined pulse-repetition rate and a predefined signal frequency, and for receiving a receive signal; 
 a signal-processing device for processing the receive signal; 
 a detection device for ascertaining a receive-signal magnitude as a noise-level sample from an envelope of the receive signal after a first predefined time duration starting with the transmit burst and within a predefined second time duration prior to a next transmit burst; 
 a threshold generation device generating a static threshold value having a predefined time characteristic; 
 a summing device generating a dynamic threshold value by summing the noise-level sample with the static threshold value; and 
 a comparator that compares the envelope of the receive signal to the dynamic threshold value and generates an output indicating that an object has been detected when the envelope exceeds the dynamic threshold value. 
 
     
     
       13. The device as recited in  claim 12 , wherein:
 the device is incorporated in an ultrasonic system for detecting surroundings of a vehicle. 
 
     
     
       14. The device as recited in  claim 12 , wherein the transmit/receive device includes a transducer for emitting the transmit burst having a signal frequency between 40 KHz and 100 KHz and for receiving an analog acoustical receive signal. 
     
     
       15. The device as recited in  claim 14 , wherein the transmit burst has a pulse length of 150 μs to 500 μs and a pulse-repetition rate of 10 Hz to 30 Hz. 
     
     
       16. The device as recited in  claim 12 , wherein the detection device has a peak-value rectifier for ascertaining the receive-signal magnitude as a function of a release by a timer. 
     
     
       17. The device as recited in  claim 12 , wherein the signal-processing device includes at least an amplifier, a band-pass filter device, a demodulation device, a two-way rectifier, and a low-pass filter, to produce a demodulated receive signal. 
     
     
       18. The device as recited in  claim 17 , wherein the static threshold value is output by the threshold generation device in response to a clock pulse. 
     
     
       19. The device as recited in  claim 18 , further comprising:
 a comparator for generating a digital detection signal by comparing the demodulated receive signal to the dynamic threshold value. 
 
     
     
       20. The device of  claim 12 ,
 wherein the detection device performs the ascertaining of the noise-level sample only during a time interval in which no reflected measuring signal from a target object occurs. 
 
     
     
       21. A method, comprising:
 transmitting an ultrasound signal at a predefined pulse-repetition interval, a predefined burst length, and a predefined signal frequency; 
 receiving a reflected signal; 
 processing the reflected signal to generate an envelope of the reflected signal; 
 sampling the envelope at a predefined time after each ultrasound signal transmission; 
 during a time interval in which no useful signals corresponding to an object to be detected contribute to the reflected signal, applying an amplitude detection procedure to the sampled envelope, thereby generating an interference signal; 
 generating a dynamic threshold by summing the interference signal with a static threshold value having a predefined time characteristic; 
 comparing the envelope to the dynamic threshold; and 
 generating an output indicating that an object has been detected when the envelope exceeds the dynamic threshold. 
 
     
     
       22. The method of  claim 21 , wherein the amplitude detection procedure is performed using a peak-value rectifier in which a hold-time constant is longer than the pulse-repetition interval, a load-time constant is longer than the burst length, and a temporal-acquisition duration is longer than the load-time constant.